1. Field of the Invention
The present invention relates to a seal for sealing along a rotatable shaft, and more particularly to a seal which includes a retainer.
2. Description of the Related Art
Conventional face contact seals, where seal rings are held in place by a shrink fit into a retainer, exhibit seal face distortion under combined thermal and pressure effects. In the current practice of seal retainer designs, there are a number of causes of seal face distortion including (1) unbalanced shrink fit contact forces developed between the retainer bore and the seal ring outside diameter, (2) pressure forces acting on the composite seal retainer shell, causing not only radial deflection but twisting motion as well, i.e., seal face non-parallelism, (3) metal bellows radial and/or axial forces at the retainer attachment location, and (4) non-axis symmetrical forces at the point of attachment to the shaft. The shrink fit forces between the seal ring insert and retainer are often a dominant cause of face distortion. These forces are due to the substantial differential thermal expansion coefficients between typical seal insert materials, such as carbon graphite and silicon carbide, and retainer materials, such as stainless steel and Inconel. Even when the seal face is lapped after assembly in the retainer, pressure and thermal conditions in operation cause severe face distortion. When the temperature of the seal assembly rises during use, the contact stress at the retainer and seal insert are reduced, and reverse distortion will occur.
The distortion caused by the above forces and the stresses imposed on conventional seals impair the life and efficiency of the seal and also consume more power as the seal distorts under differential thermal and pressure forces. Conventional seals are also subject to considerable twisting distortion a the temperature and pressure applied to the seal varies, and they are further subject to local high stress levels at the area where the retainer press fits against the seal ring.
In addition to the above problems, the inventors have found that conventional methods of attaching the seal to the shaft often add to the distortion and stresses described above.